Catalysts 2014, 4, 276-288; doi:10.3390/catal4030276

catalysts ISSN 2073-4344

www.mdpi.com/journal/catalysts

Article

Selective Hydrogenation of m-Dinitrobenzene to m-Nitroaniline over Ru-SnOx/Al2O3 Catalyst

Haiyang Cheng 1,2, Weiwei Lin 2, Xiaoru Li 2, Chao Zhang 2 and Fengyu Zhao 1,2,*

1 State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry,

Chinese Academy of Sciences, Changchun 130022, China 2 Laboratory of Green Chemistry and Process, Changchun Institute of Applied Chemistry,

Chinese Academy of Sciences, Changchun 130022, China; E-Mails: hycyl@ciac.ac.cn (H.C.);

linwei@ciac.ac.cn (W.L.); lixiaoru@ciac.ac.cn (X.L.); czhang@ciac.ac.cn (C.Z.)

* Author to whom correspondence should be addressed; E-Mail: zhaofy@ciac.ac.cn;

Tel./Fax: +86-431-8526-2410.

Received: 19 May 2014; in revised form: 23 June 2014 / Accepted: 25 June 2014 /

Published: 14 July 2014

Abstract: Series catalysts of Ru-SnOx/Al2O3 with varying SnOx loading of 0–3 wt% were

prepared, and their catalytic activity and selectivity have been discussed and compared for

the selective hydrogenation of m-dinitrobenzene (m-DNB) to m-nitroaniline (m-NAN). The

Ru-SnOx/Al2O3 catalysts were characterized by X-ray powder diffraction (XRD), X-ray

photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and hydrogen

temperature-programmed reduction (H2-TPR) and desorption (H2-TPD). Under the

modification of SnOx, the reaction activity increased obviously, and the best selectivity to

m-NAN reached above 97% at the complete conversion of m-DNB. With the increasing of

the SnOx loading, the amount of active hydrogen adsorption on the surface of the catalyst

increased according to the H2-TPD analysis, and the electron transferred from Ru to SnOx

species, as determined by XPS, inducing an electron-deficient Ru, which is a benefit for

the absorption of the nitro group. Therefore, the reaction rate and product selectivity were

greatly enhanced. Moreover, the Ru-SnOx/Al2O3 catalyst presented high stability: it could be

recycled four times without any loss in activity and selectivity.

Keywords: Ru catalyst; SnOx doping; hydrogenation; m-dinitrobenzene; m-nitroaniline;

catalyst recycling

OPEN ACCESS

Catalysts 2014, 4 277

1. Introduction

m-Nitroaniline (m-NAN) is an important intermediate for the preparation of dyes, mechanical and

electronic corrosion inhibitors, urethanes and pharmaceuticals. Generally, m-NAN is produced from

the partial reduction of m-dinitrobenzene (m-DNB) with disulfides or metal acid systems and produced

by the acetylation of aniline and then nitration, with subsequent removal of the acetyl group by

hydrolysis. Both of these two methods are hazardous, tedious and costly, with further separation and

waste disposal. From environmental and economic points of view, catalytic, selective hydrogenation of

m-DNB directly to m-NAN should be an attractive process, and it has attracted much attention in recent

years [1–3]. However, controlling the product selectivity is particularly a challenge in the hydrogenation

of m-DNB in terms of the exclusive formation of m-NAN (partial reduction product), due to it being

easily hydrogenated to the complete reduction product of m-phenylenediamine (m-PDA) [4,5] and the

formation and accumulation of intermediates, such as phenylhydroxylamine (PHA), azoxy-benzene

(AOB), azo-benzene (AB) and hydrazo-benzene (HAB), as illustrated in Scheme 1. Hence, developing

an efficient catalytic system for achieving high selectivity to m-NAN is a hot topic and has achieved

some progress. For example, over 5% Pd/C, m-NAN was obtained with a 95% selectivity at 90%

conversion at the conditions of 31 °C, 3.4 MPa H2 [1]. Over 5% Pt/C, 97% selectivity to m-NAN was

obtained at 48% conversion in supercritical CO2 at 50 °C, 16 MPa [6]. Over Pd/C and Pt/C catalysts,

the reaction condition has significant effects on the product selectivity. Supported Au catalysts, such as

Au/Al2O3, Au/Fe2O3 and Au/TiO2, could deliver 100% selectivity to m-NAN at about a 10%

conversion of m-DNB [7–10]; however, the highest selectivity to m-NAN could not achieve 90% after

conversion reached above 70%, due to m-NAN being further hydrogenated to m-PDA [5,8,11]. Ru/C

was found to be efficient in the selective partial hydrogenation of o-, m- and p-DNBs, and the

selectivities to the corresponding NANs achieved over 95% [3]. Ru/SnO2 exhibits high selectivity

(99.9%) in the hydrogenation of o-chloronitrobenzene, but the reaction rate was very low with a TOF of

4.3 × 10−2 s−1 [12]. The low activity was attributed to the high adsorption strength of the nitro group

over Ru [13]. Recently, PVP-Ru/Al2O3 was discovered to be an effective catalyst for the partial

hydrogenation of m-DNB to m-NAN with almost 100% selectivity at the conversion of m-DNB of

<95%, and the addition of a metal cation, such as Fe3+ or Sn4+, could markedly enhance the reaction

rate and retain the high selectivity of m-NAN. The interaction between metal species may change the

electronic density of the catalytic active site, thus affecting the adsorption state of the substrate on the

catalyst surface [2].

Doping a second element to the supported transition metal catalysts is considered to be an efficient

means, and a widely used one, to adjust the catalytic performance. Concerning the aforementioned

supported Ru catalysts, modification with SnOx, as an example, leads to wide applications in the

hydrogenation of aliphatic acids [14,15], esters [16–22] and α,β-unsaturated carbonyl compounds [23–27].

It is suggested that SnOx doping could improve the catalytic properties of Ru catalyst by the electronic

and geometric effects of SnOx [14,15]. Herein, we study the Ru-SnOx/Al2O3 catalysts with varying

SnO2 loading in the range of 0%–3%. The effects of SnOx on the structure and catalytic performance

of Ru-SnOx/Al2O3 catalysts are discussed in the hydrogenation of m-DNB. The catalysts are characterized

by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron

microscopy (TEM), hydrogen temperature-programmed reduction (H2-TPR) and desorption (H2-TPD).

Catalysts 2014, 4 278

Scheme 1. Possible reaction pathway for the hydrogenation of m-dinitrobenzene. m-DNB,

m-dinitrobenzene; NNSB, m-nitro-nitrosobenzene; PHA, m-nitro-phenylhydroxylamine;

m-NAN, m-nitroaniline; m-PDA, m-phenylenediamine; AOB, azoxybenzene; AB, azobenzene;

HAB, hydrazobenzene.

2. Results and Discussion

A series of supported Ru catalysts with different supports were prepared, and their catalytic

performances on the hydrogenation of m-DNB were compared. The results are listed in Table 1. The

Ru/TiO2 catalyst presented the highest catalytic activity compared with other catalysts (Entry 1); it

showed a 53% conversion in the reaction for 0.5 h with a TOF of 2142.7 h−1. Compared with Ru/TiO2,

the activity of Ru/C was a little lower (TOF, 658 h−1), and the other catalysts were quite low

(TOF < 40 h−1); they needed more than 5 h to achieve a similar conversion to that obtained with the

Ru/TiO2. However, for the catalytic selectivity to the desired product of m-NAN, the Ru/TiO2 was less

selective, while the Ru/Al2O3 was shown to be the most selective one, with selectivity above 97%

(Entry 5). It is clear that the support has a significant influence on the catalytic activity and selectivity.

Generally, a strong metal-support interaction exists in the supported noble metal catalysts, and it will

affect the performance of the active species greatly, such as for the TiO2-supported catalysts: the

electron density around the metal particles decreased as the electron transferred (or polarized) from the

metal nanoparticle to TiO2 [28–30], and the electron-deficient state of the metal nanoparticle is

favorable for the adsorption or hydrogenation of the nitro group [30–32]. Furthermore, the support has

a great influence on the adsorption and desorption of the substrates, intermediates and products. When

the formed intermediates of m-nitro-nitrosobenzene (NNSB) and PHA cannot be transferred to

m-NAN in a timely manner, they may be desorbed from the catalyst, depending on the nature of the

support, and condensed to AOB and then hydrogenated to AB and HAB, inducing a serious

accumulation of these byproducts, due to their lower transferring rate to the final m-NAN.

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Table 1. Results for the hydrogenation of m-DNB over supported Ru catalysts.

Reaction conditions: m-DNB 2 mmol, catalyst 20 mg, EtOH 20 mL, H2 4 MPa, 100 °C.

Entry Catalyst Time (h) Conversion

(%)

Selectivity (%) Rate (h−1) b

m-NAN m-PDA Others a

1 c Ru/TiO2 0.5 53.0 50.5 2.1 47.4 2142.7 2 Ru/C 1 86.0 74.8 2.9 22.3 434.6 3 Ru/SiO2 5 35.6 56.9 0.5 42.6 36.0 4 Ru/kieselguhr 5 27.2 73.2 - 26.8 27.5 5 Ru/Al2O3 5 39.2 97.4 - 2.6 39.6

a Others are the by-products, such as PHA, AOB, AB, HAB; b Reaction rate unit:

molm-DNB/(molRu·h); c Catalyst 5 mg.

To improve the catalytic activity of Ru/Al2O3, the catalyst was modified with the addition of SnOx,

and the results are shown in Figure 1. It was found that the reaction activity increased obviously with

the addition of SnOx: with the increasing of the SnOx loading from zero to 3%, the reaction rate was

linearly increased; reaching the complete conversion of m-DNB was shortened gradually from 10 to

3 h. The selectivity to m-NAN was increased also: it reached 97.3% at a complete conversion for the

catalyst with 2% SnOx, but it decreased to 91.5% for the catalyst with 3% SnOx, with the byproducts of

AOB, AB and HAB being accumulated. Therefore, the optimal loading of SnOx was 2%. The effects

SnOx on the structure of the Ru-SnOx/Al2O3 catalysts and the catalytic performance were characterized

and discussed by the results of XRD, TEM, H2-TPR, H2-TPD and XPS.

Figure 1. Selective hydrogenation of m-DNB to m-NAN over (a) Ru/Al2O3;

(b) Ru-SnOx/Al2O3-1%; (c) Ru-SnOx/Al2O3-2%; and (d) Ru-SnOx/Al2O3-3%.

Reaction conditions: m-DNB 2 mmol, catalyst 20 mg, EtOH 20 mL, H2 4 MPa, 100 °C.

(■) conversion of m-DNB; selectivity to (○) m-NAN and (∆) m-PDA; ∇and ( ) others are

by-products, such as PHA, AOB, AB and HAB.

Catalysts 2014, 4 280

From the XRD patterns in Figure 2, the diffraction peaks appeared at 37.3°, 42.6°, 46.2° and 67.3°

were attributed to γ-Al2O3 (Joint Committee on Powder Diffraction Standards (JCPDS), 13-0373), and

the peaks at 38.4°, 42.2° and 44.0° were assigned to the metallic Ru0 (JCPDS, 65-1863). With the

addition and increase of the SnOx loading, the diffraction strength of Ru was lowered, but the

diffraction peaks of the Ru-Sn alloy, such as Ru3Sn7, Ru2Sn3 or RnSn2, were not found, neither for the

diffraction peaks of SnO2 nor for those of SnO. Thus, we cannot determine the composition of SnOx,

and it may be an amorphous state existing in the samples.

Figure 2. XRD patterns of (a) Ru/Al2O3; (b) Ru-SnOx/Al2O3-1%; (c) Ru-SnOx/Al2O3-2%;

and (d) Ru-SnOx/Al2O3-3%. (●) γ-Al2O3; ∇( ) Ru0.

The TEM images and EDX spectra of supported Ru catalyst are shown in Figure 3. The average

size of the Ru particles was about 5 nm for all of the catalysts checked, indicating that the addition of

SnOx did not affect the distribution of Ru. The HRTEM images of Ru-SnOx/Al2O3-1% and

Ru-SnOx/Al2O3-2%, presented a clear and well-ordered single-crystal lattice, and the lattice spacing

was about 2.05 Å, which is the same as Ru(101) (2.055 Å). Additionally, the formation of the Ru-Sn

alloy was not detected; this is in agreement with the results of XRD in Figure 2. However, for

Ru-SnOx/Al2O3-3%, a single-crystal lattice of Ru(101) cannot be found. With the increase of the SnOx

loading, the crystallinity of Ru was lowered, and this is also in agreement with the results of XRD. The

crystallinity of Ru and the loading of SnOx may have a great influence on the adsorption and

desorption of the substrates, intermediates and products, resulting in the higher catalytic activity and

the highest selectivity to m-NAN (97.3%) at the complete conversion for the catalyst with

2% SnOx. In addition, the EDX spectra of Ru-SnOx/Al2O3-2% showed the emission of Ru and Sn,

indicating that Sn was certainly doped onto the surface of the catalyst, even though SnOx was not

detected by the XRD (Figure 2).

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Figure 3. TEM images of (a) Ru/Al2O3; (b) Ru-SnOx/Al2O3-1%; (c) Ru-SnOx/Al2O3-2%;

(d) Ru-SnOx/Al2O3-3%; and (e) the used Ru-SnOx/Al2O3-2% and (f) EDX of

Ru-SnOx/Al2O3-2%.

Figure 4 shows the H2-TPR profiles of the supported Ru catalysts and SnOx/Al2O3-2%. The

SnOx/Al2O3-2% presented a wide reduction peak at a temperature range of 100–650 °C. The reduction

peaks at 198 °C are ascribed to SnOx, which had a weak interaction with Al2O3, and the reduction

peaks at 544 °C are ascribed to tin alumina, which was formed due to the strong interaction between

SnOx and Al2O3, which is favorable to the reduction of Sn4+ to Sn2+, but inhibiting the further reduction

of Sn2+ to Sn0 [22,33]. For Ru/Al2O3, the reduction peaks at 85 °C are ascribed to Ru4+ to Ru0, with the

addition and increase of the SnOx loading; the reduction peak and zone of Ru4+ changed slightly, and

the reduction peaks at 198 °C ascribed to the overlapped SnOx and the reduction peaks at 544 °C did

not changed. This behavior also indicated that the Ru-Sn alloy was not formed. This is in agreement

with the results of XRD and TEM. Figure 5 shows the H2-TPD profiles of the supported Ru catalysts.

With the increasing of the SnOx loading, the area of the hydrogen desorption peaks increased,

Catalysts 2014, 4 282

indicating that the amount of the hydrogen adsorption increased due to the hydrogen spillover to the

surface of SnOx, resulting in an improvement of the hydrogenation activity.

Figure 4. The hydrogen temperature-programmed reduction (H2-TPR) profiles of

(a) SnOx/Al2O3-2%; (b) Ru/Al2O3; (c) Ru-SnOx/Al2O3-1%; (d) Ru-SnOx/Al2O3-2%; and

(e) Ru-SnOx/Al2O3-3%.

Figure 5. The H2-TPD profiles of the supported Ru catalysts.

The XPS spectra of the supported catalysts are shown in Figure 6. In the case of Ru, because the Ru

3d spectra overlaps with the C 1s spectrum and the Ru 3p5/2 spectrum overlaps with the Sn 3d5/2

spectrum, the Ru 3p3/2 spectrum was used to deconvolute for all of the supported Ru catalysts.

The metallic Ru at a binding energy of 462.6 eV was found for 2% Ru/Al2O3, as seen in

Figure 6a [34]. With the addition and increase of the loading of SnOx, the binding energy of Ru 3p3/2

moved to a higher binding energy, and this shifted to 463.2 eV for the sample with 3% SnOx

(Figure 6d). In the case of Sn, the binding energy of Sn 3d5/2 appeared at 487.2 eV in

Ru-SnOx/Al2O3-1%, which is ascribed to SnO; the metallic Sn and SnO2 were not observed on the

surface of the catalysts in this work, which is similar to the literature [34]. With the increasing of the

loading of SnOx, the binding energy shifted to a low value, and it moved to 486.9 eV for the sample

Catalysts 2014, 4 283

with 3% SnOx. These results indicated that an electronic interaction existed between Ru and SnOx: the

electron transferred from Ru0 to SnOx, inducing the electron-deficient state of Ru nanoparticles for the

Ru-SnOx/Al2O3 catalysts. The electron-deficient state of the Ru nanoparticle is favorable for the

adsorption of the electropositive nitrogen atom of the nitro group on the surface of the catalysts, and

so, the N=O bond was activated [30–32]. The electron-deficient state of Ru may be also favorable for

the adsorption of H2 on its surfaces, resulting in the production of more active hydrogen species [32],

thereby promoting the hydrogenation of m-DNB.

Figure 6. The XPS spectra of Ru 3p3/2 and Sn 3d of (a) Ru/Al2O3; (b) Ru-SnOx/Al2O3-1%;

(c) Ru-SnOx/Al2O3-2%; and (d) Ru-SnOx/Al2O3-3%.

Figure 7. The recycling results of Ru-SnOx/Al2O3-2% in the hydrogenation of m-DNB.

Reaction conditions: m-DNB 2 mmol, catalyst 20 mg, EtOH 20 mL, H2 4 MPa, 100 °C, 6 h.

The stability of the Ru-SnOx/Al2O3-2% catalyst was checked, as shown in Figure 7, the catalyst was

shown to be relatively stable under the reaction conditions. The selectivity of m-NAN still remained

above 97.3% in all of the recycling, although a slight decrease in the conversion appeared after the

catalyst was reused four times, which may be ascribed to the loss of the catalyst during the catalyst

separation in the recycling. For the heterogeneous catalysis, metal species leaching usually occurs

during the reaction. In this work, Ru leaching was not detected in the filtrate based on the ICP-OES

analysis with a detection limit of 0.1 ppm. Furthermore, TEM measurements showed that the Ru

particles did not aggregate, and the average size of the Ru particles remained at about 5 nm for the

Catalysts 2014, 4 284

reused sample (Figure 3e). Therefore, the developed Ru-SnO2/Al2O3-2% catalyst is an efficient

catalyst for the hydrogenation of m-DNB with satisfactory activity, selectivity and stability; it is

expected to have potential industrial applications.

3. Experimental Section

3.1. Materials

All chemicals were purchased from Aladdin (Shanghai, China); SnCl4·5H2O, Na2CO3, ethanol and

m-DNB were of analytical grade. γ-Al2O3 (170 m2/g), TiO2 (120 m2/g), SiO2 (Aldrich (Shanghai,

China), 35-60 mesh, 150 Å), active carbon (Aldrich (Shanghai, China), 100–400 mesh) and kieselguhr

were used as delivered. Gases of N2 (99.999%), Ar (99.999%) and H2 (99.999%) were purchased from

Changchun Xinxing Gas Company (Changchun, China) and used as delivered.

3.2. Catalyst Preparation

In a typical preparation, γ-Al2O3 (1.9 g) and SnCl4·5H2O (0.4 mmol) were added to 20 mL H2O and

stirred at 70 °C, then excessive Na2CO3 (1.2 mmol) in 5 mL H2O was dripped into the above solution,

and continuously stirred for 2 h. The resulting precipitates were centrifuged and washed with deionized

water and pure ethanol, respectively, and, finally, dried in vacuum at 80 °C for 6 h and calcinated in N2 at

400 °C for 2 h. In this way, SnOx/Al2O3-3% was prepared. Then, 3% SnOx-Al2O3 (0.98 g) and

RuCl3·3H2O (0.2 mmol) were added to 20 mL H2O and stirred at 70 °C. Then, excessive Na2CO3

(0.9 mmol) in 5 mL H2O was dripped into the above solution and stirred for 2 h. The resulting

precipitates were centrifuged and washed with deionized water and pure ethanol, respectively, and,

finally, dried in vacuum at 80 °C for 6 h, calcinated in N2 at 400 °C for 2 h and reduced in H2 at 300 °C

for 2 h. Thus, the Ru-SnOx/Al2O3-3% was prepared, in which the loading of Ru was about 2%, as

determined by ICP analysis.

The Ru/Al2O3, Ru/SiO2, Ru/TiO2, Ru/C and Ru/kieselguhr were also prepared by the same process

as described above, except for the addition of SnCl4·5H2O.

3.3. Catalyst Characterization

The Ru and SnOx loading in the catalysts was measured by inductively coupled plasma-optical

emission spectroscopy (ICP-OES, iCAP6300, Thermo Waltham, MA, USA). The metallic state on the

surface of the catalyst was examined by XPS (Thermo (Waltham, MA, USA) ESCALAB 250), and the

surface composition of the samples was determined from the peak areas of the corresponding lines

using origin fitting. Binding energies of the reference compounds and catalysts were measured using

the C 1s peak (284.6 eV) of the adventitious carbon as an internal standard. XRD was performed with

a D8 ADVANCE X-ray Diffractometer. TEM was performed using FEI Tecnai, G20 (Hillsboro, OR,

USA). H2-TPR and H2-TPD were carried out on the TP-5080 (Tianjin Xianquan Industry and Trade

Development Co., Ltd, Tianjin, China), with a thermal conductivity detector. Before the H2-TPR run,

50 mg of the calcinated catalyst were loaded in the quartz tube and pretreated with nitrogen at 150 °C

for 30 min. After cooling to room temperature, the sample cell was heated at a ramping rate of

10 °C/min to 800 °C in an atmosphere of a H2/Ar mixture gas (30 mL/min). For the H2-TPD test,

Catalysts 2014, 4 285

60 mg of the reduced catalyst were loaded in the quartz tube and pretreated with nitrogen at 150 °C for

30 min. After the catalyst cooled to room temperature, the absorption was conducted by flushing the

sample in a H2/Ar flow for 30 min. Then, the sample was swept with Ar for 1 h to remove physisorbed

and/or weakly bound species. H2-TPD was performed by heating the sample from room temperature to

700 °C in Ar with a ramp rate of 10 °C/min, and the TPD spectra were recorded. A liquid nitrogen trap

was used to remove water formed during the tests.

3.4. Hydrogenation of m-Dinitrobenzene

Catalytic experiments of the selective hydrogenation of m-DNB were carried out in a 100-mL

autoclave equipped with magnetic stirring. In a typical hydrogenation process, 2 mmol m-DNB, 20 mg

Ru-SnOx/Al2O3-2% catalyst and 20 mL ethanol were successively charged into the reactor. Then, the

reactor was sealed and flushed three times with N2 to remove the air. After flushing, the reactor was

heated up to 100 °C. Hydrogen (4 MPa) was introduced, and then, the reaction mixture was stirred by

an agitation speed of 1200 rpm for 2 h. It was certified that the diffusion limitation was removed

completely under the present stirring. After the reaction, the liquid products were centrifuged and

analyzed with a gas chromatograph (GC-Shimadzu-2010 (Kyoto, Japan), FID, Capillary column, Rtx-5

30 m × 0.25 mm × 0.25 μm) and identified by gas chromatography/mass spectrometry (GC/MS,

Agilent (Santa Clara, CA, USA) 5890). The GC results were obtained using an internal standard

method, and o-xylene was always used as the internal standard. For the recycling experiment, the

reaction mixture of the first run was centrifuged and separated by decantation. Then, the solid catalyst

was washed three times with solvent of ethanol, and the next run was started with the fresh m-DNB

and ethanol. The boiling points of m-DAN (283 °C), m-DNB (301 °C) and m-NAN (306 °C) were

high, and that of the condensing byproduct was much higher. Therefore, the temperature of the

injector and detector used was 320 °C, and the temperature of the oven increased from to 290 °C

(10 °C/min) and remained for 6 min at 290 °C. Under these conditions, all of the products can

be detected.

4. Conclusions

The catalytic performance of the supported Ru catalysts was compared for the hydrogenation of

m-DNB to m-NAN, and it was found that the support has a large effect on the reaction rate and product

selectivity. Ru/Al2O3 exhibits a high selectivity of >97%, but its activity is much lower compared with

the Ru/TiO2. To improve the activity, selectivity and stability, the Ru/Al2O3 was modified by doping

with SnOx. As expected, the activity of the Ru-SnOx/Al2O3 catalyst was improved significantly, and it

could remain the high selectivity to m-NAN (>97%). It was confirmed that the adsorption amount of

hydrogen increased with the increasing of the SnOx loading from H-TPD, due to the hydrogen

spillover. In addition, the electronic interaction between Ru0 and SnOx induced Ru0 to be in an

electron-deficient state, due to the transfer of an electron from Ru0 to SnOx, which is favorable for the

adsorption of the nitro group and the attack of hydrogen, resulting in high hydrogenation activity.

Moreover, the developed Ru-SnO2/Al2O3-2% catalyst is also a stable catalyst for the hydrogenation of

m-DNB to m-NAN without a loss in activity and selectivity after recycling four times. This presents

great potential for industrial applications.

Catalysts 2014, 4 286

Acknowledgments

The authors gratefully acknowledge the financial support from NSFC 21273222 and 21202159 and

from Jilin Provincial, China, 20100562.

Author Contributions

Haiyang Cheng and Fengyu Zhao contribute to the experiment design and the article writing and

revising. Haiyang Cheng also contributes to all the experimental data collection, and Weiwei Lin,

Chao Zhang and Xiaoru Li contribute to the product analysis, catalyst characterization and helpful

discussion as well.

Conflicts of Interest

The authors declare no conflict of interest.

References

1. Khilnani, V.L.; Chandalia, S.B. Selective hydrogenation. II. m-dinitrobenzene to m-nitroaniliine

using palladium on carbon as catalyst. Org. Process Res. Dev. 2001, 5, 263–266.

2. Zhao, S.L.; Liang, H.D.; Zhou, Y.F. Selective hydrogenation of m-dinitrobenzene to m-nitroaniline

catalyzed by PVP-Ru/Al2O3. Catal. Commun. 2007, 8, 1305–1309.

3. Hou, J.; Ma, Y.H.; Li, Y.H.; Guo, F.; Lu, L.H. Selective partial hydrogenation of dinitrobenzenes

to nitroanilines catalyzed by Ru/C. Chem. Lett. 2008, 37, 974–975.

4. Telkar, M.M.; Nadgeri, J.M.; Rode, C.V.; Chaudhari, R. Role of a co-metal in bimetallic Ni-Pt

catalyst for hydrogenation of m-dinitrobenzene to m-phenylenediamine. Appl. Catal. A 2005, 295,

23–30.

5. Martínez, J.J.; Rojas, H.; Vargas, L.; Parra, C.; Brijaldo, M.H.; Passos, F.B. Hydrogenation of

m-dinitrobenzene over Au catalysts on magnetic supports. J. Mol. Catal. A 2014, 383, 31–37.

6. Zhao, F.Y.; Fujita, S.; Sun, J.M.; Ikushima, Y.; Arai, M. Hydrogenation of nitro compounds with

supported platinum catalyst in supercritical carbon dioxide. Catal. Today 2004, 98, 523–528.

7. Cardenas-Lizana, F.; Gomez-Quero, S.; Keane, M.A. Gas phase hydrogenation of m-dinitrobenzene

over alumina supported Au and Au-Ni alloy. Catal. Lett. 2009, 127, 25–32.

8. Cardenas-Lizana, F.; Gomez-Quero, S.; Baddeley, C.J.; Keane, M.A. Tunable gas phase

hydrogenation of m-dinitrobenzene over alumina supported Au and Au-Ni. Appl. Catal. A 2010,

387, 155–165.

9. Cardenas-Lizana, F.; Gomez-Quero, S.; Perret, N.; Keane, M.A. Gold catalysis at the gas-solid

interface: Role of the support in determining activity and selectivity in the hydrogenation of

m-dinitrobenzene. Catal. Sci. Technol. 2011, 1, 652–661.

10. Cardenas-Lizana, F.; Gomez-Quero, S.; Jacobs, G.; Ji, Y.; Davis, B.H.; Kiwi-Minsker, L.; Keane, M.A.

Alumina supported Au-Ni: Surface synergism in the gas phase hydrogenation of nitro-compounds.

J. Phys. Chem. C 2012, 116, 11166–11180.

11. Cardenas-Lizana, F.; Gomez-Quero, S.; Idriss, H.; Keane, M.A. Gold particle size effects in the

gas-phase hydrogenation of m-dinitrobenzene over Au/TiO2. J. Catal. 2009, 268, 223–234.

Catalysts 2014, 4 287

12. Zuo, B.J.; Wang, Y.; Wang, Q.L.; Zhang, J.L.; Wu, N.Z.; Peng, L.D.; Gui, L.L.; Wang, X.D.;

Wang, R.M.; Yu, D.P. An efficient ruthenium catalyst for selective hydrogenation of

ortho-chloronitrobenzene prepared via assembling ruthenium and tin oxide nanoparticles. J. Catal.

2004, 222, 493–498.

13. Wang, X.D.; Liang, M.H.; Zhang, J.L.; Wang, Y. Selective hydrogenation of aromatic chloronitro

compounds. Curr. Org. Chem. 2007, 11, 299–314.

14. Zhu, Z.Q.; Lu, Z.H.; Li, B.; Guo, S.Z. Characterization of bimetallic Ru-Sn supported catalysts

and hydrogenation of 1,4-cyclohexanedicarboxylic acid. Appl. Catal. A 2006, 302, 208–214.

15. Wettstein, S.G.; Bond, J.Q.; Alonso, D.M.; Pham, H.N.; Datye, A.K.; Dumesic, J.A. RuSn bimetallic

catalysts for selective hydrogenation of levulinic acid to gamma-valerolactone. Appl. Catal. B 2012,

117, 321–329.

16. Ohnishi, T.; Yamakawa, T.; Shinoda, S. New preparation of Ru-Sn/Y zeolite catalyst for the

formation of acetic acid (methyl acetate) from methanol alone. Appl. Catal. A 2002, 231, 27–33.

17. Dos Santos, S.M.; Silva, A.M.; Jordao, E.; Fraga, M.A. Performance of RuSn catalysts supported

on different oxides in the selective hydrogenation of dimethyl adipate. Catal. Today 2005,

107–108, 250–257.

18. Corradini, S.A.D.; Lenzi, G.G.; Lenzi, M.K.; Soares, C.M.F.; Santos, O.A.A. Characterization and

hydrogenation of methyl oleate over Ru/TiO2, Ru-Sn/TiO2 catalysts. J. Non-Cryst. Solids 2008,

354, 4865–4870.

19. Silva, A.M.; Morales, M.A.; Baggio-Saitovitch, E.M.; Jordao, E.; Fraga, M.A. Selective

hydrogenation of dimethyl adipate on titania-supported RuSn catalysts. Appl. Catal. A 2009, 353,

101–106.

20. Miyake, T.; Makino, T.; Taniguchi, S.; Watanuki, H.; Niki, T.; Shimizu, S.; Kojima, Y.; Sano, M.

Alcohol synthesis by hydrogenation of fatty acid methyl esters on supported Ru-Sn and Rh-Sn

catalysts. Appl. Catal. A 2009, 364, 108–112.

21. Echeverri, D.A.; Marin, J.M.; Restrepo, G.M.; Rios, L.A. Characterization and carbonylic

hydrogenation of methyl oleate over Ru-Sn/Al2O3: Effects of metal precursor and chlorine

removal. Appl. Catal. A 2009, 366, 342–347.

22. Mazzieri, V.A.; Sad, M.R.; Vera, C.R.; Pieck, C.L.; Grau, R. Preparation and characterization of

Ru-Sn/Al2O3 catalysts for the hydrogenation of fatty acid methyl esters. Quim. Nova 2010,

33, 269–272.

23. Hajek, J.; Kumar, N.; Salmi, T.; Murzin, D.Y.; Karhu, H.; Vayrynen, J.; Cerveny, L.; Paseka, I.

Impact of catalyst reduction mode on selective hydrogenation of cinnamaldehyde over Ru-Sn

sol-gel catalysts. Ind. Eng. Chem. Res. 2003, 42, 295–305.

24. Hajek, J.; Murzin, D.Y. Liquid-phase hydrogenation of cinnamaldehyde over a Ru-Sn sol-gel

catalyst. 1. Evaluation of mass transfer via a combined experimental/theoretical approach.

Ind. Eng. Chem. Res. 2004, 43, 2030–2038.

25. Hajek, J.; Maki-Arvela, P.; Toukoniitty, E.; Kumar, N.; Salmi, T.; Murzin, D.Y.; Cerveny, L.;

Paseka, I.; Laine, E. The effect of chemical reducing agents in the synthesis of sol-gel Ru-Sn

catalysts: Selective hydrogenation of cinnamaldehyde. J. Sol-Gel Sci. Technol. 2004, 30, 187–195.

26. Springerova, J.; Kacer, P.; Cerveny, L. Selective hydrogenation of alpha,beta-unsaturated carbonyl

compounds on supported Ru-Sn catalysts. Res. Chem. Intermed. 2005, 31, 785–795.

Catalysts 2014, 4 288

27. Riguetto, B.A.; Rodrigues, C.E.C.; Morales, M.A.; Baggio-Saitovitch, E.; Gengembre, L.; Payen, E.;

Marques, C.M.P.; Bueno, J.M.C. Ru-Sn catalysts for selective hydrogenation of crotonaldehyde:

Effect of the Sn/(Ru + Sn) ratio. Appl. Catal. A 2007, 318, 70–78.

28. Li, D.; Ichikuni, N.; Shimazu, S.; Uematsu, T. Hydrogenation of CO2 over sprayed Ru/TiO2 fine

particles and strong metal-support interaction. Appl. Catal. A 1999, 180, 227–235.

29. Li, X.H.; Zheng, W.L.; Pan, H.Y.; Yu, Y.; Chen, L.; Wu, P. Pt nanoparticles supported on highly

dispersed TiO2 coated on SBA-15 as an efficient and recyclable catalyst for liquid-phase

hydrogenation. J. Catal. 2013, 300, 9–19.

30. Lin, W.W.; Cheng, H.Y.; Ming, J.; Yu, Y.C.; Zhao, F.Y. Deactivation of Ni/TiO2 catalyst in the

hydrogenation of nitrobenzene in water and improvement in its stability by coating a layer of

hydrophobic carbon. J. Catal. 2012, 291, 149–154.

31. Zhang, J.L.; Wang, Y.; Ji, H.; Wei, Y.G.; Wu, N.Z.; Zuo, B.J.; Wang, Q.L. Magnetic nanocomposite

catalysts with high activity and selectivity for selective hydrogenation of ortho-chloronitrobenzene.

J. Catal. 2005, 229, 114–118.

32. Zhao, Y.F.; Zhang, H.Y.; Huang, C.L.; Chen, S.; Liu, Z.M. Pt/Titania/reduced graphite oxide

nanocomposite: An efficient catalyst for nitrobenzene hydrogenation. J. Colloid Interface Sci.

2012, 374, 83–88.

33. Mazzieri, V.A.; Grau, J.M.; Yori, J.C.; Vera, C.R.; Pieck, C.L. Influence of additives on the Pt

metal activity of naphtha reforming catalysts. Appl. Catal. A 2009, 354, 161–168.

34. Thepkaew, J.; Therdthianwong, S.; Therdthianwong, A.; Kucernak, A.; Wongyao, N. Promotional

roles of Ru and Sn in mesoporous PtRu and PtRuSn catalysts toward ethanol electrooxidation.

Int. J. Hydrogen Energy 2013, 38, 9454–9463.

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